1. Field of the Invention
The present invention relates to a method for conducting redundancy checks in a chain network, more particularly, to establishment of a redundancy mechanism in the chain network, in which the communication ports of a first switch and a second switch are set to be forwarding and blocking respectively, so that when an link break happens to the chain network, the two switches close to the break point will send control packets to the first and second switches respectively to forwarding the port that is originally blocking, thus allowing the network to return to normal state quickly.
2. Description of the Prior Art
With quick changes in IT and vigorous developments on Internet technologies, network technologies are utilized to help people to communicate with each other beyond boundaries. Progress in such regard not only brings more conveniences to the public, but also provides enterprises with a more cost-effective way of production.
However, due to instability of network devices, production may be interrupted, causing heavy losses to enterprises. Therefore, a focus of network architecture in an enterprise is how to develop the ability of restoring a network reliably and quickly in case of disconnection.
A solution to network outages as stated above is to supplement backup network devices in the network architecture to establish a redundant environment. However, the presence of these backup devices will easily cause looping of the network, which will further lead to such problems as broadcast storm, simultaneous receipt of the same packets by a single network device and instability of the MAC address of the network device. Under such circumstance, switches will learn and change the address uninterruptedly, and the burden on microprocessors of the network devices will increase. Currently, IEEE802.1D—Spanning Tree Protocol (STP)—is adopted to eliminate these problems. Yet in an STP environment, when it is necessary to start backup devices in response to any network device failure, it will take longer recalculation time to recover the network to its normal state. In order to shorten the time to live, IEEE adopts the new 802.1W—Rapid Spanning Tree Protocol (RSTP)—to reduce the recalculation time by shortening the time for conversion of the connection port state and setting up an alternate port.
However, both STP and RSTP is a tree network topology. If the tree topology is too big with too many network devices (i.e. network nodes), it will cause the backup devices to respond at a lower speed. So the tree topology will limit the number of nodes in a single network. For practical applications of industrial control devices, once the network crash long time, it will cause heavy losses or serious incidents. Recently, the industry environment often uses a ring network; however, when a redundancy technology be set up in the ring network, the increasing node of the ring network occurs higher recovery time and lower reliability, Therefore, multi ring network topology is adopted to meet the requirements for quicker recovery capability and more network nodes in a single network. Refer to FIG. 8, which shows redundant system in ring networks. In this figure, ring network A consists of a plurality of switches A1˜A5, while ring network B includes a plurality of switches B1˜B5. For example, if the redundancy technology such as a ring coupling system is set up among a plurality of ring networks, the port of the switch A5 that connects the port of the switch B1 will be forwarded, while the port of the switches A4 that connects the port of switches B2 will be blocked. Ring coupling is utilized to forwarding state the port of the switches A4 that connects the port of switches B2 automatically when the switches A5 and B1 cannot communicate. Though the above-mentioned network recovery capability is more effective than STP and RSTP, however, the ring coupling system is more complex to set up between the ring networks and reduce network reliability.
Compared to the strict requirement for network stability in industrial control, the reliability of such network operation is rather low. And if this redundancy mechanism is adopted by enterprises in ring networks for production and manufacture, it will increase the risks that network devices are incompatible with each other and cannot transmit data among them or the machine cannot work continuously. All these will have great impact on enterprises' profits and long-term benefits.
Therefore, how to eliminate the conventional problems and disadvantages is what the firms involved in this industry needs urgently to research and improve.